Vat dyeing process



United States Patent ,0

2,742,340 VAT DYEING PROCESS No Drawing. Application September 6, 1951,

Serial No. 245,423

12 Claims. C1. 8-34 This invention relates to an improved method of dyeing with vat dyes and more particularly to a high temperature vat dyeing process.

Since the advent of high speed, high temperature, continuous dyeing, a new requirement has been imposed on vat dyes, namely, one of stability in their leuco form to temperaturesapproaching the boil. Many vat dye colors, otherwise highly desirable because of their. particular shade, fastness, and other properties have been found to be unstable at the temperatures employed in many of the newly developed vat dyeing processes. This sensitivity to high temperatures results in dyeings which are uneven, specky and weak and, in general, of an uneven and in ferior shade. This may be due to over-reduction or-incomplete reduction of the vafidyestuff, instability and decomposition at th e'lhigh temperatures, ,etc.

According to one aspect .of the present invention, it

a has been found that the defects occurring whendyeing with thermally'unstable vat dyeslimleuco form, particularly at temperaturesranging,from about .150". to2'2 11,; may be corrected by ma'intainingihe reduction potential. in the leuco dye bath at a predetermined; pptirnurn value.

by the gradual controlled addition to the dyebath of appropriaterediicing substan stablizing substances and alkali It will of coursebe understood that'this process maybe employed in applying any leiuco vat dyes at any suitable temperatures. The process is followed by the usual finishing or oxidizing treatments. The'ter'm dye bath in this disclosure andathe appended claims is employed to include the usual.bath icontaining a solution of the vat dyestufi' in reduced leu co and in which the fibrous material is dyed, and also those cases in which stufi, while yielding a most desirable shade, has been 2,742,340 Patented Apr. 17, 1956 found to be particularly sensitive to high temperatures.

In such cases, of course, the addition of stabilizing sub-v stances is called for. The preferred reduction potential range is in most cases about 930 to 1050 mv.

Fibrous materials to which the process is applicable are all those materials which are susceptible to coloration by vat dyeing processes. Such materials may be in any suitable form, as for example, fabrics, yarns, ropes, warps, fibers, filaments and the like, The process is applicable to various types of vat dyeing methods, as for example, continuous dyeing, jig dyeing (piece work), Beck open vat dyeing, package dyeing, and the like. a a

The instant invention is applicable to vat dyeing processes in general, employing any suitable temperatures and pressures, but it is most efiective in the high temperature application of thermally unstable vat dyestuffs such as the dianthraquinone dihydroazines. Thus, the process is also advantageously employed in applying dye-.- stufis such as Indanthrene Blue BFP (CI 1113), Algol Orange RF (CI 1217), IndanthreneBrilliant Violet 2R (C1 1104), IndanthreneBlue RS (CI 1106), Indanthrene BlueGC (C1 1112), Indanthrene Olive R (CI 1150), 2,2 8-diethyl-2, 2-bianthra [1,9] pyrazole-6,6(2H,2'H)- dione,4,l0-dibromodibenzo [0, d, j, k] pyrene-6,12-dione,

1 tetrabromo 8,16- pyranthrenedione, trichloro N,N'-diphenyl-3,4,9, 10aperylene-tetracarboxylic dimide, 3-(1- anthraquinononylamino) anthra [9, 2, l-a m n] naphth- [2, 3-h] acridine-5, .10, 15 (l6H)-trione and the products, disclosed in U. S. Patents 1,706,902';f1,758,3 65; 1,790,780; l,7 90,843;.-1,803, 757; 1,832,209; 1,845,469; 1,851,082; 1,877,315; 1,877,945; 1,885,172; 1,904,145; 1,931,821; 1,943,710; 1,945,484; 1,949,209; 2,086,843; 2,118,192;

' 2,123-,251;'2,22s,445; 2,238,209and mixtures thereof.

The control of the reductionpotential of the dye bath canbe maintained by following the..course of the reducfibrous material is'first padded or impregnated with the dyestuif and then treated with a reducing material in another operation. In the; latter case, the bath at or in thefiber contains both the reducing ,substance and the dyestuff, and is thus essentiallyafidye bathfii. t As suitable reducing substances maybe mentioned tioned sugars, dextrins,-inorganic-nitrites and other sub stances whose reduction; potentialsdo not exceed that of the reducing substance employed.

. predetermined value for the particular type o f dyeing being" carried out, the stabilizing agent feed is activated or in- It will be understood that other agents may be added totthe aforementionedsubstances for their known functions, such -jas salt and the like.

It has been found that at redhetioii potentialsbelow about 750 mv. (when measuredby meansof a" saturated calomel-platinum electrode system) d eingsmaybe obtained which are uneven, specky and weakduetothe incomplete reduction of the v'at dyestutt and in such cases an increase in the amount of reducing substances added is called for. about 1,100 mv. the shade may ,become inferior, .presumably due to over-reduction ofthe vat dyestuif which would'tend toward oxanthrone formation, particularly At reduction potentials greater than'i in'the case of Indanthrene' Blue BC (C1113) which'dyevalue for producing'the desired results 7 tion with a calomel-platinum electrode system in turn connectedto a recording potentiometer. By means of this system,"one'is able to anticipate thefneedi for eitherl reducing agent or protective agent depending on the a The control of thelfee d' of the alkali, reducing agent and stabilizing agent may 1 be manual or automatic and, of'course, automatic. control nieasuredreduction potential.

is preferable Where possible; By way of example, the

recordingpotentiometer may: be connected throughgautomatic control means well known per se to separate feed systems for' the alkali-sodium"hydrosulfite or otherredue" ing agent and for the dextrin, sodium nitrite or other fs't'a bilizing or protecting agent in such a manner that when themeas'ured reduction potentialexceeds the optimum creased and when the measured reduction potential falls below the optimum value, the reducing agent feed, is

activated or increased Thereducing agent, such as sodium hydrosulfite, is ordinarily added together with a, predetermined amount of' caustic, potash, or the like.

In someinstances, however, the reducing agent alone may be added when needed 'to keep the reduction potential of the bath at the optimum predetermined value, and alkali added only when it is found that addition of the reducing agent alone does not produce the desired -in crease in reduction potential. The reducing material may comprise a mixture of reducing agents, and similarly, the stabilizing or protective material may comprise 'a mixture of stabilizing :agents.

mixture, and in such cases,'the mixture is only added to the dye bath or reducingbath when the measured reduction potential talls below the optimum predetermined In some cases it is preferable to add the reducing and stabilizing agents together in one It of coursebeunderstood that although the above described saturated calomel-platinum electrode system is preferred for measurement of the reduction potential in accordance witlrthe invention; other suitabl'esystems may be ,used. While the millivolt valuesof the reduction potential measured by other systems may, because of use of different referenceelectrodes or other causes, differ from the valuesrecommended he'reinbefore, it should be apparent that the actual value of the reduction' potential to be employed in any particular. instance for obtaining the best results-will? be the same regardless of the measuringsystem employed. Accordingly, the: operative reduction potential range for use in the'pre'sent invention may be expressed; as a value equivalent to from about 750- to 1100. mv'. whensmeas'ured by means of a saturated calomel platinum electrode. system.

The use of soluble inorganic nitrites, particularly sodiumnitrite; as: stabilizing substances in vat dye baths to prevent over-reduction has been recently proposed. It has been found however that use of' these nitrites is attended with various difficulties, chief among which is the fact that their full protective or stabilizing action is only developed in the bath after reduction has proceeded for sometime. This lag in the stabilizing activity of the nitrit'e's results in over-reduction of the initial portions of the dyed fibrous material. Nor can this difiiculty be readily corrected 'by the practice of initially charging increased amounts of nitrite (up to- 500% or more of the amountof nitrite otherwise required), since although this remedies the aforementioned initial over-reduction, the increased stabilizing or protective activity later developed so retards proper reduction of the dyestufi that subsequent portions of the dyed fibrous material are found to .be incompletely reduced. These difliculties are especially pronounced inthe case of many presently employed rapid continuous dyeing processes, in which uniform level dyeings from the beginning to the end of the runs may not thereby be obtained.

Applicant has made the discovery that the aforementioned difliculty in obtaining adequate protective or stabilizing action against initial over-reduction may be remedied by initially charging hydroxylamine into the dye bath in addition to the amount of nitrite found to be sufficient for the-subsequent stabilization or protection ofthe reducing process. In this manner initial and subsequent protection is obtained, with consequent advantageous results'with respect to the dyeings produced.

The hydroxylamine is preferably added inthe form of its salts; as for example hydroxylammonium sulfate,

. This is made possible by the fact that the exact amounts of materials necessary for replenishing the bath to maintain its reducing action maybe thus-instantaneously determined andadded as needed. The-excess material usually added as a-safety factor to allow for errors caused by the hereto-- fore relatively crude estimations of the requirements. of the dye bath based on resultant shades and past experience isthereby saved. The dyeings obtained are uniform and highly acceptable from both a scientific and commercial aspect.

The following examples are merely illustrative of the inventionand are not. to. be: regarded as limitative;

Example 1 V Aistirred" solution of oh. sodium hydroxide in 2% gallons of water was heated'to 180 F.fand 2 /2 oz. Indanthrene Blue BFP' (dichloro dianthraquinone dihydroazine) were added. After a few minutes the dyestuff was dispersed. Two electrodes for measurement of the oxidation-reduction potentials were inserted in the bath (the electrodes were a measuring [platinum] electrode and a saturated calomel [mercury-mercurous chloride-saturated RC1] reference electrode).

At zero minutes there were added213 g. of dextrin and 142 g. of sodium hydrosulfit'e', and the reduction potential as measured by a Beckrn'anpI-I- meter .(whose range had been extended by the additionof 'a bucking potential) and recorded on a Brown recorder was found tobe 972 mv. The Beckrnan pH meter is a well known high input impedance indicator. 5

After five minutes, the potential had gradually dropped to 964 mv. The potential'was maintainedat about 180 F. for 90 minutes between 950 and 960 millivolts by the addition of dry hydrosulfite (total 240 g. in almost a continuous manner) and dextrin- (total 160g. in 10g. portions). Addition of hydrosulfiteincreased the reductionpotential while addition of dextrin impeded increase ofth'ereduC- tionpotential. In this'ex'peri'rnent dextrin was added when the potential increased toa9 5 -5 or 960- mv.

Cotton swatches (8 dyeings) were dyed at about ten minute intervals. The swatches were found to be dyed uniformly when the potential was held in the range of Example 2 A mill trial involving 2,000 yards of cloth was carried out under the following conditions:

White broadcloth was paddedthrough a suspension of Ind; Blue BFP (1 1b./gal.), squeezed and thendeveloped continuously in: a Williams Unit (see U. S; Patent 2,364;-

838} containing the following initial charge: 3 /2 -oz'./'gal. sodium hydroxide 3 /2 02/ gal. sodiumhydro'sulfite 0:2 oz./ gal. hydroxylammonium' sulfate 0.2 oz./g'al. sodium nitrite 0126 oz./'gal. Ind. Blue BFP A tenipjeratureof 200-208 was maintained throughout the run. The potential measured asin Example 1 was 1025 mv. The potential wasmaintained throughout the Conc. of pad bath:

-- 0.87 oz./gal. Ind. Blue BFP 0.125 oz./ gal. dimethoxyviolanthrone Composition of developing bath:

1.53 oz-Jgal. sodium hydroxide 1.4 oz./gal. sodium hydrosulfite 0.1 oz./gal. hydroxylarnmonium sulfate 0.1 ozz/gal. sodium-nitrite 0.014 oz./gal Ind. Blue- BFP 0.002- oz./ gal. dirnethoxyviolanthrone 'Was. excellent and the amountsofchemicals required Example4 A mill trial involving 750 yards ofFortisan (Stretched,

saponified jcellllloseacetate) was carried out under the following conditionsz,

26 lbs. of a vat dyestufi of theformula;

9 lbs. 12 oz. of a vat dyestulf of the formula;

1 lb. oz. of Ind. Golden Orange GA Double Paste (C1 1096) were vatted with 14 lbs. sodium hydroxide and 14 lbs. sodium hydrosulfite in 110 gal. H2O for 10 minutes at 120 F.

The resulting vat was used to dye 750 yards of Fortisan (prepared for dyeing by a brief pretreatment in 6% caustic solution at 60-70 F.) on a jig for 8 ends at 15 minutes per end. The first two ends were run at 120 F. and the last six ends at 130 F. A reduction potential of 990-1025 mv. measured as in Example l of the appended claims.

was maintained throughoutthe runs by addingv 4 lbs. sodium hydroxide and 7 lbs. sodium hydrosulfite in increments as needed. In (this example, the hydroa The dyeing obtained was of excellent quality, shade,

fastness, levelnes's and uniformity.

Various modifications and variations of this invention will be obvious to. a person skilled in the art and'such variations and modifications are to be regarded as with in the purview of this application and the spirit and scope I claim:

1. In a process of vat dyeing fibrous materials in a vat containing dyestufi, a reducingsubstance therefor, alkali, and an inorganic nitrite, the improvement comprising initially adding hydroxylamine to the vat in a molar ratio of nitrite to hydroxylamine of from about 1:2 to 4: 1.

2. A continuous process for vat dyeing fibrous materials comprising the steps of impregnating the fibrous material with vat dyestuif, passing the fibrous material continuously through a reducing bath containing caustic, sodium hydrosulfite, sodium nitrite and hydroxylamine, and continuously replenishing the reducing bath with a supply of caustic, sodium hydrosulfite and sodium nitrite. i

3. In a process of vat dyeing fibrous materials, the improvement comprising maintaining the reduction potential, during dyeing, in the dyebath, which has been initially charged with vat dyestulf, reducing substance, sodium nitrite, and hydroxylamine, at a value equivalent to from about 750 to 1100 mv. when measured by means of a saturated calomel-platinum electrode system connected to a high input impedance indicator by the gradual controlled addition to the dyebath of a reducing substance and sodium nitrite.

4. The process of claim 3 wherein the sodium nitrite and hydroxylamine in the initial charge are in a molar ratio of from about 1:2 to 4: 1.

5. In a process of vat dyeing fibrous materials, the improvement comprising maintaining the reduction potential, during dyeing, in the dyebath, which has been initially charged with vat dyestufi, reducing substance, sodium nitrite, and hydroxylamine, at a value equivalent to from about 750 to 1100 mv. when measured by means of a saturated calomel-platinum electrode system connected to a high point input impedance indicator by con tinuously measuring the reduction potential in the dyebath, and by adding a reducing substance and sodium nitrite when the measured potential falls below the desired value.

6. The process of claim 5 wherein the sodium nitrite and hydroxylamine in the initial charge are in a molar .ratio of from about 1:2 to 4:1.

substance and sodium nitrite when the measured potential falls below the desired value.

8. The process of claim 7 wherein the sodium nitrite the improvement comprising maintaining the reduction potential, duringv dyeing, in the reducing bath which has been initially ehargedwithsaid dyestufi, caustic, sodium hydro sulfite, sodium nitrite and hydroxylamine at about 1025 mv. by continuously measuring the reduction potential therein by means of a saturated calomel-platinumelectrode system connected to a high: input impedance indicator and adding caustic, sodium hydro sulfite and.

sodium nitrite when the measured potential falls below about 1025 mv. V

10; The process ofi claim 9 wherein. the sodium nitrite and; hydroxylamine in the initial charge are in a molar ratio of from about 1:2 to: 4:1.

7 11'. In a-p'rocess of vat dyeing. fibrous materials by impregnating with a mixture of dichloro dianthraquinone dihydroazine and dimethoxyviolanthrone and reducing at a temperature from about 200 to- 205 R, the improvement comprising maintaining. the reduction potential during" dyeing in tlie reducin'g bath whichlias been initially charged with. said vat dyestufis jcaustic sodium hydrosulfi'te, sodium nitritefand hildi-oztylttmineat from about 940 to 955 mv. by continuously t measuring tlie reduction potential therein by' rn'eans of a sa'turated'j calomel-platinum-electrode' systlem connected to a high input impedance indicator and adding caustic, sodium hydro sulfite and sodium nitrite when the measured potential tends to fall below 940 mv.

1 2. The process of claim- 11' wherein the sodium nitrite and hydroxylamine' in the initial charge are in a molar ratio of from about 1:2 to 4:1.

References Cited in the file of this patent OTHER REFERENCES American Dyestufl Reporter for December 12, 1949, pgs. P919 to P922, inclusive. 

1. IN A PROCESS OF VAT DYEING FIBROUS MATERIALS IN A VAT CONTAINING DYESTUFF, A REDUCING SUBSTANCE THEREFOR, ALKALI, AND AN INORGANIC NITRITE, THE IMPROVEMENT COMPRISING INITIALLY ADDING HYDROXYLAMINE TO THE VAT IN A MOLAR RATIO OF NITRITE TO HYDROXYLAMINE OF FROM ABOUT 1:2 TO 4:1. 